Ron Paul is now tied with Newt Gingrich for the lead in Iowa, which will hold the nation's first caucus on Jan. 3. Paul's hard-hitting ads attacking Gingrich may account for Gingrich's decline in the new poll.

Gingrich, a former speaker of the House, has the support of 22 percent of likely caucus goers, according to a poll released Tuesday by Public Policy Polling. That represents a five-point drop from the previous week. Texas Congressman Paul, at 21 percent, saw a three-point bump from the previous week.

The Paul campaign has been running well-produced contrast ads against Gingrich, charging him with “serial hypocrisy,” in Iowa. The ads accuse Gingrich of profiting from the housing crisis due to the money he received from Freddie Mac.

Gingrich says he was a paid consultant; Paul accuses him of being a lobbyist for the company. The ad also insinuates that Gingrich supported an individual mandate to purchase health insurance because of the consulting fees he received from health insurance companies, which would profit from such a mandate.

Paul has some advantages over Gingrich in the Iowa caucus fight. To win a caucus, candidates must have well-organized, passionate followers, which describes Paul's supporters well. When asked if they were strongly committed to their choice, or might change their mind, Paul came out on top with 29 percent of his supporters saying they are strongly committed. Gingrich, on the other hand, only recently surged to the lead in national polls and is just now starting to build an organization in Iowa.

Gingrich has the highest number of supporters, 26 percent, who voted in the Republican caucus in 2008. Paul, on the other hand, has the highest number of supporters, 34 percent, who voted in the Democratic caucus in 2008. Gingrich also did best, at 31 percent, among those who said they were favorable toward the “GOP establishment,” and Paul did best, 34 percent, among those who were unfavorable toward the “GOP establishment.” This suggests that Gingrich is doing well at mobilizing the Republican base, whereas Paul is doing better at expanding the Republican base.

Paul's disadvantage, the poll indicates, is that most of his supporters are young and have never before been to a caucus. Paul had the highest number of supporters, 22 percent, that did not vote in the 2008 caucus. Paul's strongest support, 42 percent, also came from those aged 18 to 29. Gingrich, on the other hand, has the most support among those aged 45 to 65 (27 percent) and those over 65 (25 percent).

The most reliable caucus voters are those who are older and those who have been to a caucus before. There is a precedent, however, for winning the Iowa caucus with young, new voters. That is how President Obama won in 2008.